This invention relates generally to CCD (charge coupled device) imaging and particularly to a method for avoiding the identification of perimeter variations as blemishes in the proximity of the perimeter of an image on a CCD.
U.S. Pat. No. 4,454,545 issued to R. A. Duschl discloses a CCD based inspection system.
U.S. Pat. No. 4,575,751 entitled "Method and Subsystem for Plotting the Perimeter of an Object" issued to R. A. Duschl now U.S. Pat. No. 4,575,751discloses a system for plotting the perimeter of an image cast onto a CCD. The image pixels immediately adjacent to the perimeter pixels are identified and their addresses held in memory irrespective of the orientation of the image and the size of the image.
U.S. application Ser. No. 663,153 entitled "Method For Detecting Blemishes Near The Perimeter Of A CCD Image" filed on even date herewith by Edward Cohen, discloses a method for detecting blemishes in the proximity of a perimeter plotted by the system disclosed in R. A. Duschl U.S. Pat. No. 4,575,751.
These disclosures are incorporated herein by reference.
The systems described in the above-referenced applications and patent are quite satisfactory for the purposes intended. However, difficulties sometime arise because the perimeters being plotted are not perfectly straight and thus do not perfectly lie along the rows or columns of the CCD. Instead, the perimeters typically vary across several rows or columns of pixels. The method described in application Ser. No. 663,153 detects blemishes in the proximity of the perimeter. However, in some instances permissible perimeter variations can be identified as blemishes and acceptable perimeters can be rejected. For this reason, there is a need for a method for distinguishing permissible perimeter variations from blemishes in the close proximity of the perimeter of an object cast onto a CCD. The instant invention fulfills this long felt need.
The present invention is cast into the environment of detecting the perimeter of a black matrix on the inside surface of a CRT faceplate panel. This environment was selected when describing the present invention because the invention is an improvement of the inventions described in the referenced patent and patent applications and those inventions are described in that environment. Nevertheless it will be understood by those skilled in the art that the present invention is useful in distinguishing permissible perimeter variations from blemishes in the proximity of the perimeter of any image cast onto a CCD.